I can confirm this observation. I've made a quick test. I've rendered the same scene in Bryce 5.5 (correct behaviour) and Bryce 7.1 ('effect of boolean operation'). You can compare the look of light sensitive material below.
One alternative is to use volumetric material with 'basic shading' option checked and low density - it looks the same in the both versions of Bryce - in fact it should behave more physically correct than the 'light' option. If you don't want dimming - there's an additive option.